Microsoft Access: Enforcing referential integrity, the cascade options, and orphan records 

In this short screencast we'll examine why we enforce referential integrity on one-to-many relationships, and why it doesn't always mean that no orphan records exist. We'll explain how and why to use the Cascade Update Related Fields option as well as the Cascade Delete Related Records option.
We'll discuss why enforcing referential integrity prevents the creation of NEW orphan records by not allowing you to delete a record in the "one" table that has matching records in the "many" table.
We'll also discuss why enforcing referential integrity prevents the creation of NEW orphan records by not allowing you to enter bogus values in the foreign key field of the "many" table.
Finally, we'll discuss how enforcing referential integrity does not always mean that there are no orphan records given a null (nothing) value in the foreign key field can exist when referential integrity is applied to a relationship.